1. Field of the Invention
The present invention relates generally to systems for fusing or joining conduit or piping sections, such as polyvinyl chloride piping and, in particular, to a fusion process for effectively and permanently joining a first conduit portion to a second conduit portion.
2. Description of Related Art
Conduit systems are used in many applications throughout the world in order to transfer or convey material, such as water and other fluids, from location to location for distribution throughout the system. For example, extensive conduit systems are used to distribute water to both residences and businesses for use and further processes. Typically, such conduit or piping systems are located underground, as aboveground piping would be both unsightly and intrusive.
In general, water conduit systems transport material through piping manufactured from various materials, e.g., cast iron, ductile iron, reinforced concrete, cement-asbestos, etc. The pipes are buried underground, with the branches extending in various directions in order to reach the end user. Normally, after many years of use, or for some other reason, the in-ground piping fails and begins to leak, thereby reducing line pressure and unnecessarily allowing water to leak into the area surrounding the piping. Such leaks not only affect the system, but also increase the processing costs of the supplier, which, in turn, increases the end user costs. Therefore, these leaks must be quickly repaired and preventative measures taken to ensure that further leakage is prevented.
Due to the underground position of the conduit system, repairing a leaking pipe is particularly labor intensive and time consuming. Trenches must be dug along the pipeline to locate the leak and effectively repair it prior to putting the pipe back in service. Various lining systems have been developed according to the prior art in an attempt to seal a leaking pipe or a pipe that has fallen into disrepair, whether to repair a present crack or to preventatively ensure against future cracks or breaks. In addition, a method whereby a much smaller diameter pipe within the larger diameter cracked or broken pipe has been used. However, this merely replaces the problem of a cracked outer pipe with a cracked or otherwise leaking inner pipe. Still further, using such a pipe-in-pipe system drastically reduces the flow through the conduit system and evidences unwanted and varying pressure parameters.
To that end, a pipe liner and method of installation have been developed, as disclosed in U.S. Pat. No. 5,794,662 to St. Onge et al., specifically directed to pressurized pipeline applications. The St. Onge patent is directed to a method of relining sewer lines, water lines or gas lines, and uses a segmented liner of reduced size relative to the pipe being relined. However, as opposed to merely leaving the small diameter liner conduit within the large diameter outer conduit, the method of the St. Onge patent uses heat and/or pressure to mold the reduced size pipe to the shape of the pipe being relined. In particular, the inner or liner conduit is a thermoplastic pipe, typically a polyvinyl chloride (PVC) pipe that, when exposed to heat or pressure, expands and molds against the inside of an existing conduit to effect the relining of it. This process allows for both the lining of the entire length of pipe or only a portion of it that is damaged, which is typically referred to as “spot repair.”
According to the St. Onge patent, once the length of the liner conduit is inserted into the existing or host conduit, the liner conduit is plugged at either end and exposed to steam under pressure to heat the liner conduit along its length and apply pressure, which urges it to expand and contact the interior walls of the surrounding host conduit. Once the liner conduit has fully expanded to conform to the interior surface of the existing conduit, it is cooled and the plugs are removed. The resulting expanded liner conduit conforms to the walls of the host conduit, thereby preventing any further leakage. Also, the method of the St. Onge patent requires only trenches to be dug at either end of the section to be repaired.
While the St. Onge patent represents an advance in the art of relining or repairing underground conduit systems, there is room in the art for additional improvements and advancements. Specifically, in order to transport and insert the liner conduit within the host conduit, the liner conduit must be manufactured in sections or portions, which are typically much shorter in length than the final and intended liner conduit length. Therefore, portions of the liner conduit must be connected onsite as the liner conduit is fed into the host conduit. In addition, there is a need for the ability to connect multiple lengths of the liner conduit via a joint having the strength of the original conduit and which does not increase the diameter of the joint area beyond the original conduit diameter. The use of multiple and connectable conduit pieces is useful in many different applications beyond the above-discussed expansion application. For example, the use of multiple and fused conduits is particularly useful in the case of sliplining, wherein a slightly smaller diameter fused conduit is inserted into a larger pipe that is in need of rehabilitation, but that does not require a full capacity for flow. In this case, the conduit is pulled in and left in place, but is not expanded. In most cases, the space between the conduit and the host pipe is filled with a low-strength grout to hold the new line in position. However, the sliplining process may require the use of lines that could accommodate a larger diameter coupling or mechanical joint.
Fused conduit is also required in various other applications, such as in a rehabilitation application, wherein the fused joint is used in connection with a horizontal directional drilling process. This method drills a pilot hole in the ground and can be steered in a precise manner to control elevation and alignment. After the pilot hole is complete, the drill hole is reamed to a larger diameter and filled with drill mud to hold the larger hole open. The drill casing is then pulled through the drill mud resulting in a conduit in place. However, this process requires a larger drill to accommodate the mechanical couplings and joints manufactured from PE or HDPE.
Further, fused conduit is useful in a pipe bursting application. Pipe bursting uses a large hydraulic or pneumatic cutter head to break apart old pipe and force the pieces into the surrounding soil. This allows a new pipe of equal or larger diameter in the existing line to be pulled in. This process is used where the new line capacity must be substantially increased. Also, of course, fused pipe is equally useful in a direct-bury application.
Fusion processes for pipe or conduit have been developed that utilize mechanical joints, embedded wires at or near the fusion joint or resistive heating elements for joining conduit sections together. For example, see U.S. Pat. No. 6,398,264 to Bryant, III; U.S. Pat. No. 6,394,502 to Andersson; U.S. Pat. No. 6,156,144 to Lueghamer; U.S. Pat. No. 5,921,587 to Lueghamer; U.S. Pat. No. 4,684,789 to Eggleston; and U.S. Pat. No. 4,642,155 to Ramsey. Polyethylene pipe (PE or HDPE) has been routinely fused for many years. For example, see U.S. Pat. No. 3,002,871 to Tramm et al.; U.S. Pat. No. 4,987,018 to Dickinson et al.; U.S. Pat. No. 4,963,421 to Dickinson et al.; and U.S. Pat. No. 4,780,163 to Haneline, Jr. et al. and U.S. Patent Publication No. 2003/0080552 to Genoni. Accordingly, preexisting fusion equipment is available. However, this equipment must be modified in its use and operating parameters for fusion of polyvinyl chloride-based conduit. Unlike polyethylene pipe, which is generally joined by heat fusion techniques, PVC pipe has normally been limited to applications that can be serviced by bell-and-spigot joints. This limitation has restricted the use of PVC pipe in sliplining rehabilitation applications. Therefore, there is a need in the art to provide an essentially single piece of PVC liner conduit starting stock with no mechanical joints, which does not increase the diameter of the starting stock as a mechanical coupling would. Such a coupling or fused joint must have similar strength characteristics as the original conduit and preclude infiltration in joints, by eliminating such mechanical joints. In addition, it may be preferable to provide a coupling that is capable of withstanding a subsequent expansion process for eventual use in a pressurized conduit system.